Oscillator with stabilized feedback



Oct. 27, 1942.

J.- N. WHITAKER OSCILLATOR WITH STABILIZED FEEDBACK F- iled Sept. 5,1940

INVENTOR MUVI/ ATTORNEY Patented Oct. 27, 1942 OSCILLATOR WITHSTABILIZED FEEDBACK James N. Whitaker, Weehawken, N. 3., assignor toRadio Corporation of America, a corporation 7 of Delaware ApplicationSeptember 5, 1940, Serial No. 355,437

4 Claims.

This invention relates to oscillation generating systems, andparticularly to a mechanically controlled oscillation generating system.

A primary object of the present invention is to provide a source ofoscillations of constant frequency and constant amplitude.

Another object is to provide such a. source which is particularlyadaptable for use in the audio frequency range below ten thousandcycles.

A further object is to provide a system for generating oscillations ofconstant frequency and constant amplitude which is compact andsubstantially unaffected by temperature changes.

A further object is to provide a low frequency electrical source ofconstant frequency and constant amplitude of output which may beoperated from the standard power supply systems regardless of the usualfluctuations in voltage encountered in such a system.

A still further object is to provide a low frequency oscillationgenerator with means for rectifying the components of the output energyand for dividing this energy into positive and negative components, theenergy of said positive components being dissipated in a resistor andthe negative components applied to the grid of a limiter tube therebymaintaining a grid potential on said limiter tube variable betweencathode potential and a more negative potential, said limiter tube beingused for supplying feed-back energy to the frequency-determining meansby which the oscillation generator proper is coritrolled.

In general, the foregoing objects are achieved by the provision of atuning fork having a driving magnet and a pick-up magnet, the drivingmagnet being coupled to the output circuit of a limiter tube, while thepick-up magnet is caused to feed control potentials to the grids of atwin triode amplifier tube. One section of this twin triode is used tosupply feed-back energy to the limiter tube, while the other section ofthe twin triode is used to amplify the oscillations generated and tosupply the amplified oscillations to a succeeding stage ofamplification, the output circuit of which is coupled to any desiredutilization device. In circuit with the grid of the limiter tube Ipreferably employ a double diode tube for rectification purposes. Thistube has the function of dividing the wave derived from one section ofthe twin triode amplifier into its positive and negative components, thenegative component of said wave being subsequently applied to the gridof the limiter tube, while the positive component is dissipated in asuitable as resistor. It is found in practice that the stability of thesystem is greatly increased by providing a constant fork driving poweras is accomplished with the aid of the aforesaid double diode rectifiertube. The range of amplitude in the power delivered to the load resistorI may be made as wide as the ratio of 9 to l'without seriouslydisturbing the stability of the system.

The improvements in low frequency oscillation generators as hereinset'forth may be compared with earlier forms of such oscillators,typical of which is that disclosed in my Patent No. 2,144,- 236, grantedJanuary 17, 1939. In the system which I disclosed in that patent thegrid of a limiter tube was driven positive and the'limiting action onthe positive half cycles was obtained by plate current saturation. Sincethe point of saturation is dependent to a large extent upon the filamentemission, a variation in driving power was liable to occur as a resultof changes in the cathode heater potential.

In the present system the heretofore encountered difiiculties have beenovercome by the use of a high mu tube as a limiter device, and the gridpotential of this tube is caused to vary from zero to a negative value.'A component of the positive half cycles of the generator is caused topass through one-half ofv the twin diode rectifier and through asuitable load resistor to ground so as to utilize the charge on acoupling condenser across which energy is fed back to the driving coilfor the tuning fork.

The plate current of the high mu limiter tube is quite low even withzero bias on its grid. Saturation, therefore, is never reached, as theemission from the cathode maybe considerably in excess of that requiredfor the small plate current permitted by a high resistance in the platecircuit of the limiter tube.

My invention is illustrated in more detail in the accompanying drawing,wherein Figure 1 shows a circuit diagram of one embodiment of theinvention, and

Fig. 2 shows a modification of a portion of th circuit arrangement shownin Fig. 1.

Referring to Fig. 1, Ishow a'tuning fork I having a driving coil 2 and apick-up 0011.3.

Merely by way of illustration the tuning fork is indicated as thoughdesigned for vibration at a frequency of 600 cycles per second. Thepickup coil 3 has one end grounded and the other end leads to the twogrids of a twin triode tube 4. Amplification takes place in this tube insuch manner that the outputs from bothsections are in phase. Thev twocathodes ofthe tube 4 are j ode-resistor 22.

interconnected and are grounded through a cathode resistor 21. In shuntwith this resistor is a suitable capacitor 28.

The output circuit which includes the anode is fed with direct currentpotential from any suitable source 6, this circuit including a resistorl for the purpose of resistance coupling to the grid of a limiter tube 8across coupling condenser 9. The output circuit of the limiter tube 8may also be supplied with anode potential from the source 6 fed throughthe resistor 10. This resistor, by way of illustration, may have a valueof the order of 200,000 ohms.

The driving coil 2 for the tuning fork is grounded at one end and isconnected through a resistor H and a coupling condenser l2 to the outputcircuit of the limiter tube 8.

The cathode of the limiter tube 8 is grounded and is also connectedthrough a resistor [3 to one anode I4 of the twin diode tube [5. Theother anode 16 of this tube is connected to the grid ofthe limiter tube8, and'al'so to thecathode opposite the anode l' l'intlie tube 15. Theremaining cathode of this twin 'diode I5 is connected through a resistorH 'to ground. With the circuit connections as shown, and due to the factthat resistors 13 and Ill are of substantially different values, thegrid of the limiter tube 8 is prevented from being driven more positivethan the potential of its cathode. It's bias is, therefore, varied onlybetween zero and some suitable negative value. The effect of thisarrangement is to cause the limiter tube '8 to deliver a substantiallysquare wave for energizing the magnet 2 whereby the tuning fork isdriven.

The twin triode tube 4, "as heretofore mentioned, includes 'a sectionwhich is useful for amplification ofthe energy whichis'applied to afurther stage'o'f amplification and then coupled to a utilizationcircuit. In this portion of the twin triode tube 4 is an anode 18.Direct current is supplied to this "anode across resistor [9. Thiscircuitis resistanc'e coupled'to the grid of an amplifier'tube 20.coupling condenser 2! being provided. The cathode of the amplifier tube'20 is'connected to ground through a cath- This resistor is preferably'in shunt'with a capacitor '23. The biasing circuit for'the tube20'iriclude's preferablyan inductive impedance 24 in shunt with acondenser'25. The inductance 24 and'capacitance 25 form a-tank circuitwhichmay be tuned tothefrequency of the oscillations generated.

The output circuit of the tube20 includes the primary of atransformer*26. The secondary of this transformer maybeconnected to anysuitable utilization device.

Referring now toFig. 2 I show a modification of the circuit arrangementof Fig. 1. The double diode discharge tube 30 of'Fig. 2'is substitutedfor a similar tube 1'5 in 'Fig. l. A portionof the circuit arrangementofliigyl Whichis'included in a dotted line enclosure may be bodilyreplaced by the circuit arrangement shown in Fig. 2. The

details of Fig. 2'will now be described.

The output circuitwhich is connected to the anode 5' in the tube4 iscoupled by means of the capacitor 9 to the cathode 32 and also to theano'de'33 in the'tube30. The anode 3| in this tube is connected directlyto the control grid in the tube 8 and is also connected through acathode resistor l3 to the grounded cathode of the tube '8. The positivewave peaks impressed 33 and 34, this path being completed to groundthrough the resistor ll. The negative wave peaks produce a space currentbetween the electrodes 3| and 32 such that the grid of the tube 8becomes negatively biased. Variations in this bias are, therefore,dependent upon the amplitude of the negative wave peaks and consequentlythe limiter tube 8 will operate in dependence upon the control as givenby these rectified negative impulses, thereby delivering a suitablevalue of feed-back energy across the capacitor I2 for exciting thedriving coil 2 which is in association with the tuning fork.

It will be observed from the showing in the drawing as well as from theabove description that the grid of the limiter tube 8 receives nopotential at all or a negative potential, which bias is, therefore,varied only between zero and some suitably negative value.

Those skilled in the art will appreciate that whether my invention 'iscarried out 'by one or the other of the two alternative embodiments asshown and described the objects and advantages of the invention will beattained. It Will also be understood that other modifications may bemade without departing from the spirit of the invention. This inventionitself is therefore to be regarded as though limited only in accordancewith the claims.

I claim:

1. "In a mechanical vibratorof the type which generates low "frequencyelectrical oscillations, an amplifier for 'saido'scillations,-a secondstage amplifier for a'utilizableoutputcorhponent from the first saidamplifier, a feed-back circuit effective to sustain oscillations in saidvibrator, said feed-back circuit including a discha-rge 'tube having acathode, a control grid and an anode, means coupled to said anode forexciting said vibrator, a capacitor for feeding controlpotentialsfrom'the first said amplifier to the control grid'ofsaid-discharge tube,-and'means connected in circuit between saidcathodeand-said control grid for maintaining --a bias on said grid-whichvaries only between "zeroand a negative value with respect to thecathode, the last said *means comprising a 'double diode rectifier tube,said rectifier tube having "a-cathode-and-a non-opposing anode-connected 'to the control 'grid of the discharge tube in'said 'feedback' circuit, the remaining electrodes being connected throughindependent {parallel-disposed resistors to the cathode of the dischargetube in said feedback circuit,'said resistors-being unequal in value.

'2. A constant frequency, constant amplitude oscillation generatorhaving a feed-'back-circuit, a 'd'ischarge'tube the 'space-path-of whichis -includedin isaid feed-back circuit, said tube having an inputcircuitconnected betweenits cathode and its control grid, and being "controlledby a potential applied thereto fro'msaid generator, said input circuitincluding a fullwave rectifier of the four-terminal type having two'ofits oppositely poled terminals-for'respectively different unilaterallyconductive paths connected to'said' control grid, and the remainingterminals connected respectively to resistors of unequal value,-andmeans"for maintaining the terminals of said resistors remote from saidrectifier at thepotential-of-said cathode, thereby topreventthebiasapplied tothe control grid of said tube from becoming positivewith'respect cuit including an electromagnetic exciter means for saidgenerator and including an electron discharge tube amplifier thecathode-anode circuit of which is coupled to said exciter means, acontrol grid for the tube of said amplifier, a double diode tube havingthe cathode of one of its space paths and the anode of the other of itsspace paths both connected to said control grid, a resistive connectionof predetermined value in circuit between ground and the anode of thefirst said space path in said double diode tube, a resistive connectionof lesser than said predetermined value in circuit between ground andthe cathode of the second said space path in said double diode tube, anda ground connection to the cathode of said amplifier tube, thecombination so defined being such that the control grid of saidamplifier tube is prevented from being driven positive with respect toits cathode.

4. An oscillation generator having a mechanical vibrator,electro-magnetic means for exciting said vibrator, electro-magneticmeans for deriving output potentials from said vibrator, electronicmeans having two output circuits for amplifying said potentials, autilization device coupled to one of said output circuits, a feedbackcircuit coupled to the other of said output circuits, an amplifier insaid feed-back circuit, said amplifier having a grounded cathode andbeing arranged to feed a pulsating current to said exciting means, andmeans including a full wave rectifier having'its unidirectional pathsoppositely faced toward ground connections of unequal impedance, thejunctions between two terminals of said unidirectional paths beingconnected to said amplifier grid, :for causing the grid of saidamplifier to be controlled by potentials which vary only between a zerovalue and a negative Value with respect to the cathode of saidamplifier. JAMES N. WHITAKER,

